The CBER maintains and distributes a reference immune globulin for measles and poliomyelitis antibody potency assays. The present reference, Lot 175, was established in 1971. As supplies of this material are almost exhausted, we have undertaken the standardization of new reference. Approximately 3000 two-ml vials of Immune Globulin (Human) were purchased from Armour Pharmaceutical for this purpose. Samples of this proposed reference and of Lot 175 were distributed to nine laboratories for comparative testing. These laboratories performed assays for antibodies to poliomyelitis types 1, 2 and 3 and to measles, comparing the proposed reference to Lot 175, so that minimum levels for these antibodies in Immune Globulin and Immune Globulin Intravenous could be established. In addition, the laboratories also compared the hepatitis A antibody (anti-HAV) content of the proposed reference to the WHO reference, and the anti-HBs level to that of HBIG Reference Lot 2. Thus, if at some later date it is decided to replace the present minimum requirement for polio antibody content with one for anti-HAV, a suitable reference preparation will be available. It was also deemed appropriate to establish a low-titer anti-HBs reference material in order to provide a standard for Immune Globulin and Immune Globulin Intravenous. We have also performed comparative assays of HBIG Lot 2 and the WHO anti-HBs reference. These materials were derived from the same parent material, but the WHO reference is lyophilized and is reconstituted to a final protein concentration of about one-half that of HBIG Lot 2. Comparison of the anti-HBs levels in these materials indicated that Lot 2 contains 238 + 17 IU/ml (the WHO reference is defined to contain 100 IU/ml). The protein concentrations in Lot 2 and the WHO reference were determined to be 17.27% and 8.33%, respectively, so that the ratio of Lot 2 to WHO (as determined by relative protein content) is 2.07. By this determination, then, Lot 2 should contain 207 IU/ml.